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PM1B > Fundamental Organic Chemistry > Flashcards

Fundamental Organic Chemistry Flashcards

1
Q

What is an S orbital?

A

They are the lowest energy orbitals and can accommodate 2 electrons

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2
Q

What is a P orbital?

A

There are 3 P orbitals; Py, Px and Pz. Each one is dumb-bell shaped. All three are degenerate (equal in energy) and each can accommodate 2 electrons (6 in total)

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3
Q

What is a D orbital?

A

Orbitals important in transition metal chemistry. There are d orbitals, all are degenerate and can each accommodate 2 electrons (10 in total)

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4
Q

State the Aufbau principle

A

Orbitals of lowest energy are filled first

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5
Q

State the Pauli Exclusion principle

A

Only 2 electrons can occupy the same orbital

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6
Q

State Hund’s rule

A

If 2 or more empty degenerate orbitals are available, one electron is placed in each until they are all half full

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7
Q

What is a covalent bond?

A

They are bonds formed when 2 or more atoms share electrons

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8
Q

What is a covalent bond?

A

They are bonds formed when 2 or more atoms share electrons

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9
Q

What is a sigma bond?

A

A bond that occurs due to P-P overlap and the electron density is between the nuclei

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10
Q

What is a pi bond?

A

A bond that occurs due to P-P overlap but the electron density is not between the nuclei, it is above and below the plane.
These are higher energy bonds as the nuclei can “see” each other so there is no repulsion.
The two atomic orbitals involved cannot achieve maximum orbital overlap.

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11
Q

Why is hybridisation theory useful and how does it work?

A

It is useful for explaining why carbon atoms in different environments are different shapes.
-generate an excited state of carbon by promoting an electron from the 2S orbital to the 2P orbital.
-there are now 4 unpaired electrons that can bond
-BUT they are not degenerate.
(basically making 2S and 2P into one orbital- SP3)
-SP3 orbitals are higher in energy than the S orbitals but lower in energy than the P orbitals.

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12
Q

Describe carbon in SP3 hybridisation

A
  • Tetrahedral
  • bond angle of 109.5 degrees
  • carbon with 4 sigma bonds are SP3 hybridised (methane, ethane)
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13
Q

Describe carbon in SP2 hybridisation

A
  • Trigonal planar (due to repulsion between bonding orbitals)
  • 3 sigma bonds and 1 pi bond
  • P orbital is perpendicular to the plane
  • bond angle is 120 degrees
  • eg ethene
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14
Q

Describe carbon in SP hybridisation

A
  • Linear (due to repulsion of bonding orbitals)
  • 2 sigma bonds and 2 pi bonds
  • bond angle is 180 degrees
  • eg ethyne
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15
Q

When do the Hybridisation theory rules apply?

A

The rules only hold true if the carbon is uncharged and has a full valence shell.

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16
Q

What state would you find carbocations in?

A
  • SP2 hybridisation
  • 6 valence electrons so 3 areas of negative charge which makes a trigonal planar shape.
  • the empty P orbital is the highest energy orbital
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17
Q

what state would you find carbanions in?

A
  • SP3 hybridisation
  • 8 electron species
  • 3 sigma bonds and 1 lone pair of electrons.
  • all electron containing orbitals are as far apart as possible
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18
Q

Describe carbon in SP3 hybridisation

A
  • Tetrahedral
  • bond angle of 109.5 degrees
  • carbon with 4 sigma bonds are SP3 hybridised (methane, ethane)- single bonds
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19
Q

Describe carbon in SP2 hybridisation

A
  • Trigonal planar (due to repulsion between bonding orbitals)
  • 3 sigma bonds and 1 pi bond
  • P orbital is perpendicular to the plane
  • bond angle is 120 degrees
  • eg ethene (double bonds)
20
Q

Describe carbon in SP hybridisation

A
  • Linear (due to repulsion of bonding orbitals)
  • 2 sigma bonds and 2 pi bonds
  • bond angle is 180 degrees
  • eg ethyne (triple bonds)
21
Q

what state would you find carbanions in?

A
  • SP3 hybridisation
  • 8 electron species
  • 3 sigma bonds and 1 lone pair of electrons.
  • all electron containing orbitals are as far apart as possible
22
Q

what state would you find carbanions in?

A
  • SP3 hybridisation
  • 8 electron species
  • 3 sigma bonds and 1 lone pair of electrons.
  • all electron containing orbitals are as far apart as possible
23
Q

Describe hybridisation in ammonia

A
  • Ammonia is isoelectronic with methane
  • Bonding angles in methane are 109 degrees but not in ammonia- still SP3 hybridised as the lone pair has an effect
  • the lone pair takes up more space than a bonding pair therefore the N-H bonds are pushed closer together
  • H-N-H bonding angle is 107.5 degrees
24
Q

Describe hybridisation in water

A
  • water is isoelectronic with both ammonia and methane
  • SP3 hybridised
  • The 2 lone pairs take up more space therefore the O-H bonds are pushed closer together
  • Bond angle is 104 degrees
25
Q

What are antibonding orbitals?

A

Orbitals that are in the opposite phase and in a different location to the bonding orbitals.
They are always higher in energy than the corresponding bonding orbital.
Putting electrons into an antibonding orbital breaks the bonding orbital.

26
Q

What is electronegativity?

A
  • A measure of an atoms ability to pull electrons towards itself
  • increases from left to right across the periodic table
  • decreases from top to bottom
  • flourine is the most electronegative element
27
Q

A bond can be polarised one way or another due to the elctronegativity of the adjacent element, what are the implications of this?

A
  • In the sigma bond and the pi bond the largest orbital coefficient (electron density) is on the more electronegative element as it is more stabilised
  • but in the sigma* and the pi* orbitals the opposite is true, so the largest orbital coefficient is on the less electronegative element (*=antibonding)
28
Q

A bond can be polarised one way or another due to the elctronegativity of the adjacent element, what are the implications of this?

A
  • In the sigma bond and the pi bond the largest orbital coefficient (electron density) is on the more electronegative element as it is more stabilised
  • but in the sigma* and the pi* orbitals the opposite is true, so the largest orbital coefficient is on the less electronegative element (*=antibonding)
29
Q

Define isomerism

A

Different compounds which have the same molecular formula

30
Q

Define constitutional isomers

A

Compounds with the same molecular formula but a different connectivity of the atoms.
eg. C2H6O- ethanol and dimethyl ether. same molecular formula but very different chemical and physical properties.

31
Q

Define constitutional isomer

A

Compounds with the same molecular formula but a different connectivity of the atoms.

eg. C2H6O- ethanol and dimethyl ether. same molecular formula but very different chemical and physical properties.
- another example is the xylenes, these are referred to as positional isomers

32
Q

Define steriosomer

A

Compounds with identical constitution but differing in the arrangement of their atoms in space.

33
Q

What is an achiral molecule?

A

A molecule that is superimposable on its mirror image form.

34
Q

What is a chiral molecule?

A

A molecule that is non-superimposable on its mirror image. All that is required for a molecule to be chiral is a tetrahedral carbon that has 4 different groups attached.

35
Q

What is an enantiomer?

A

A chiral molecules mirror image.

36
Q

What is a racemic mixture?

A

When both enantiomers are present in equal amounts. If there is more of one enantiomer than the other then the mixture is said to be enantiomerically enriched.

37
Q

Define the term Absolute configuration

A

The spatial configuration of atoms in a chiral molecule whcih distinguish it from its enantiomer

38
Q

State the Cahn, Ingold, Prelog rules for chiral centres

A
  1. the four substituents surrounding the chiral centre are ranked from 1-4
    - rank according to decreasing atomic number
  2. the lowest ranked group is orientated furthest away from the observer
  3. determine whether the remaining substituents:
    - decrease in priority in a clockwise direction- R
    - decrease in priority in an anticlockwise direction- S
39
Q

State the Cahn, Ingold, Prelog rules for chiral centres

A
  1. the four substituents surrounding the chiral centre are ranked from 1-4
    - rank according to decreasing atomic number
    - a higher mass isotope takes priority over a lower mass isotope
    - where 2 atoms are the same, the atomic number of the second (or 3rd or 4th etc) atom away from the chiral centre determines the ranking
    - double or triple bonds are treated as if they were split into 2 or 3 single bonds respectively (ghost carbons)
  2. the lowest ranked group is orientated furthest away from the observer
  3. determine whether the remaining substituents:
    - decrease in priority in a clockwise direction- R
    - decrease in priority in an anticlockwise direction- S
40
Q

What are double bond isomers also called?

A

Geometric isomers

41
Q

State the Cahn, Ingold, Prelog (CIP) rules for chiral centres

A
  1. the four substituents surrounding the chiral centre are ranked from 1-4
    - rank according to decreasing atomic number
    - a higher mass isotope takes priority over a lower mass isotope
    - where 2 atoms are the same, the atomic number of the second (or 3rd or 4th etc) atom away from the chiral centre determines the ranking
    - double or triple bonds are treated as if they were split into 2 or 3 single bonds respectively (ghost carbons)
  2. the lowest ranked group is orientated furthest away from the observer
  3. determine whether the remaining substituents:
    - decrease in priority in a clockwise direction- R
    - decrease in priority in an anticlockwise direction- S
42
Q

What are double bond isomers also called?

A

Geometric isomers

43
Q

Explain how you would distinguish between a trans and a cis isomer.

A

If 2 hydrogens are on the opposite side of the double bond it is described as trans. If they are on the same side it is described as cis.

44
Q

Explain how you would distinguish between an E and Z isomer.

A
  • Divide the double bond into 2 seperate sides
  • rank the substituents into 1 and 2 using CIP rules
  • if the two highest ranked substituents are on opposite sides then it is E
  • if they are on the same side then it is Z
45
Q

What are the 4 steps to naming an organic molecule?

A

1.Find the parent hydrocarbon- longest continuous straight chain
2.Number the atoms in the main chain- begin from the end nearest a branch
3.Identify and number subtituents
4.Write out the name
-Prefix-parent-suffix
Prefix- where the substituents and functional groups are located
parent- how many carbons there are in the main chain
suffix- what functional groups are present

PM1B (2 decks)

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